Top quark pair property measurements and $t\bar{t} + X$ using the ATLAS detector at the LHC

Abstract

Measuring the properties of the top quark has been proven to be a reliable test of the Standard Model of particle physics (SM). At the Large Hadron Collider, top quark physics has entered the era of precision measurements which allows to measure new top quark properties and to repeat other top quark properties measurements with improved precision. This article presents the measurements of top quark spin observables, charge and CP asymmetries, $W$ boson polarisation from $t\bar{t}$ events and the cross section of $t\bar{t}$ pairs produced in association with a $W$ or $Z$ boson. All these measurements are using data from proton-proton collisions taken with the ATLAS detector at the Large Hadron Collider. The spin correlation $C(n,n)$ is measured for the first time and direct CP violation is measured directly for the first time in the context of $b$-hadron decays. The measured value of the CP mixing asymmetry $A^b_\text{mix}$ presented here cannot disprove the deviation in the dimuon asymmetry seen by the D0 experiment. The $W$ boson polarisation measurement from $t\bar{t}$ events is the most precise one to date and is used to constrain anomalous couplings at the $Wtb$ vertex. All results are in agreement with the SM predictions.